What term describes imperfections in timber caused by branches growing within the tree?

• A. Cracks
• B. Knots
• C. Warp
• D. Grain

Answer: (B)

Knots are imperfections that form where a branch grew from the trunk while the tree was alive. As the timber forms, the branch becomes embedded in the wood, creating a knot—a patch where the grain changes direction and density around the branch. This interrupting of the smooth, uniform grain can create weak spots or complicate machining, especially if the knot is large or tight.

This differs from cracks, which are splits caused by stress; warp, which is distortion from drying or moisture; and grain, which describes the overall direction of the wood fibers. The term that describes imperfections caused by branches growing within the tree is knots.